Polymeric materials for indwelling devices that can resist biofilm formation and encrustation over long time periods are presently in high demand.
One region of the body that is of particular interest is the urinary system. In theory, the colonization of an indwelling-device surface with urease-producing bacteria will lead to the hydrolysis of urea into ammonium and carbonate, causing alkalinization of urine in the vicinity of the device. The higher pH environment in turn lowers the solubility of struvite and hydroxyapatite found within the urine, leading to the formation of deposits on the device surface. Clinical and experimental studies have focused on several treatments to avoid the formation of such deposits, including the following: (a) acidification of urine, (b) modification of the device surface to provide a smoother and more hydrophilic surface (using, for example, lubricious hydrophilic coatings, phospholipid coatings or surfactant coatings), and (c) formation of surface coatings with one or more antimicrobials (for example, urinary stents have been immersed in antibiotic or prior to use and have been provided with antimicrobial coatings).
These efforts, however, have been ineffective to significantly prolong the half-life of indwelling stents. In general, the proportion of the stent covered with biofilm increases with time, as does the degree of encrustation. Moreover, studies have shown that adherent bacteria inside the biofilm are resistant to antimicrobial treatments. Typically, the doses required to kill biofilm bacteria (e.g., adherent bacteria protected by a glycocalyx biofilm matrix) is many times the dose required to eradicate planktonic bacteria (i.e., non-adherent bacteria). Such elevated doses are also typically toxic to the patient.